Influence of additive and subtractive zirconia and lithium disilicate manufacturing on tensile bond strength and surface topography.

STATEMENT OF PROBLEM: Although bonding is important for long-term clinical success, studies on the bonding of additively manufactured ceramics are sparse. PURPOSE: The purpose of this in vitro study was to determine the influence of manufacturing methods, additive (LCM) versus subtractive (CAM). and ceramic materials, zirconia (ZrO2) and lithium disilicate (LiSi), on the tensile bond strength (TBS), failure mode, and surface roughness of ceramics. MATERIAL AND METHODS: A total of 240 ceramic specimens (n=60/group; 2×2×10 mm) were prepared. Two additively manufactured (LCM-printed) ceramics, LiSi and ZrO2 (Lithoz), subtractively manufactured LiSi (IPS e.max CAD), and subtractively manufactured ZrO2 (KATANA Zirconia HTML PLUS) were evaluated. From each material, 40 specimens were bonded together (n=20 ceramic-ceramic specimens/group), and 20 specimens were bonded to equally sized human dentin specimens (n=20 ceramic-dentin specimens/group). The ZrO2 specimens were airborne-particle abraded (Al2O3, 50 µm, 0.1 MPa), and the LiSi specimens were etched with hydrofluoric acid. Then, a universal primer (Monobond Plus) was applied. After the dentin was coated with an etch-and-rinse adhesive (Syntac Classic), the specimens were bonded with luting composite resin (Variolink Esthetic DC), light polymerized for 40 seconds, thermally aged (10 000 cycles between 5 °C and 55 °C), tested for TBS, and statistically analyzed (1- and 3-way ANOVA and Weibull analysis). The ceramic surface was examined with scanning electron microscopy, and surface roughness was measured with digital microscopy before and after surface pretreatment. RESULTS: TBS varied between 5.88 ±2.22 MPa and 6.34 ±2.26 MPa in the ceramic-dentin groups and 12.40 ±1.56 MPa and 18.82 ±5.92 MPa in the ceramic-ceramic groups. No significant difference was observed regarding the manufacturing method and material for different bonding conditions (P>.05). Additive and subtractive LiSi showed the highest reliability with m=18.27. The ceramic-ceramic specimens failed cohesively in the luting composite resin, whereas the ceramic-dentin specimens failed adhesively. CONCLUSIONS: The manufacturing method and material used had little effect on bond strength values or surface properties. The recently introduced printed materials performed similarly to conventionally milled materials.

Influence of Immediate Dentin Sealing on Marginal Gaps of Laminate Veneers: Machinable Monolithic Zirconia Versus Pressable Lithium Dislocate. An In Vitro Study.

PURPOSE: To investigate the influence of immediate dentin sealing (IDS) vs delayed dentin sealing (DDS) on the marginal gaps of machinable monolithic zirconia (MMZ) vs pressable lithium disilicate (PLD) laminate veneers. MATERIALS AND METHODS: A total of 40 maxillary lateral incisors were used and received butt-joint laminate veneer preparation. The samples were divided into two groups (n = 20 each) according to ceramic material: PLD ceramic was used in the first group, and MMZ was used in the second. Each group was then divided into two subgroups according to the bonding protocol: IDS was employed in one, and DDS in the other (n = 10 each). The marginal gap widths were measured using digital microscopy and statistically analyzed. RESULTS: The smallest marginal gaps were observed in MMZ-DDS (57.2 ± 8.4 µm), followed by PLD-DDS (62.4 ± 2.7 µm) and MMZ-IDS (63.5 ± 1.9 µm). The largest marginal gaps were observed in PLD-IDS (81.5 ± 6.3 µm). Two-way ANOVA revealed that the bonding technique (P < .001) and ceramic material (P < .001) both showed significant differences. CONCLUSIONS: MMZ produced beIer marginal accuracy than PLD. IDS seems to have a predisposition to significantly wider marginal gaps than DDS, but these gaps are within the clinically acceptable range. The marginal accuracy of ceramic veneers appears to be related to the bonding technique as well as the material of construction.

Influence of Immediate Dentin Sealing on the Marginal Gaps of Laminate Veneers: Machinable Monolithic Zirconia Versus Pressable Lithium Disilicate: An in vitro study.

PURPOSE: To investigate the influence of immediate dentin sealing (IDS) vs delayed dentin sealing (DDS) on the marginal gaps of machinable monolithic zirconia vs pressable lithium disilicate laminate veneers. MATERIALS AND METHODS: A total of 40 maxillary lateral incisors were used and received butt-joint laminate veneer preparation. The samples were divided into two groups (n = 20 each) according to ceramic material: pressable lithium disilicate ceramic (PLD) was used in the first group, and machinable monolithic zirconia (MMZ) was used in the second. Each group was then divided into two subgroups according to the bonding protocol: IDS was employed in one, and DDS in the other (n = 10 each). The marginal gap widths were measured using digital microscopy and statistically analyzed. RESULTS: The smallest marginal gaps were observed in MMZ-DDS (57.2 ± 8.4 µm), followed by PLD-DDS (62.4 ± 2.7 µm) and MMZ-IDS (63.5 ± 1.9 µm). The largest marginal gaps were observed in PLD-IDS (81.5 ± 6.3 µm). Two-way ANOVA revealed that the bonding technique (P < .001) and ceramic material (P < .001) both showed significant differences. CONCLUSIONS: MMZ produced better marginal accuracy than PLD. IDS seems to have a predisposition to significantly wider marginal gaps than DDS, but these gaps are within the clinically acceptable range. The marginal accuracy of ceramic veneers appears to be related to the bonding technique as well as the material of construction.

Effects of application method on shrinkage vectors and volumetric shrinkage of bulk-fill composites in class-II restorations.

OBJECTIVES: Upon initial proximal wall construction, the favorable C-factor of class-II cavities may become unfavorable. This study investigated the application method on bulk-fill resin composite polymerization shrinkage. METHODS: Occluso-proximal class-II cavities were prepared in 40 molars and bonded with a self-etch adhesive (Adhese Universal). The study groups varied according to the resin composite application: group-1: bulk application, Tetric EvoCeram Bulk Fill (TBF); group-2: proximal wall construction (TBF) and occlusal cavity filling (TBF); group-3: thin flowable liner layer, Tetric EvoFlow Bulk Fill (TEF) and bulk filling (TBF); group-4: flowable liner (TEF), proximal wall (TBF), occlusal cavity (TBF); and group-5: bulk application, SDR (3 mm) and capping layer (TBF, 1 mm). Each resin composite increment was scanned twice using micro-CT (uncured, cured 40 s) at a resolution of 16 µm. Shrinkage vectors and volumetric polymerization shrinkage were evaluated and statistically analyzed (one-way ANOVA). SEM images were used to investigate the tooth-restoration interface. RESULTS: Shrinkage vectors differed significantly among the groups and were greatest in gp5-fl/SDR (47.6 µm), followed by gp1-TBF (23.8 µm) and least in gp5-fl/SDR+TBF (11.1 µm). Volumetric shrinkage varied significantly with the use of SDR (gp5-fl/SDR: 2.6%) and TEF (gp4-fl/TEF: 2.5%) to TBF (gp4-fl/TEF+wl/TBF: 0.6%) in the incremental application. SIGNIFICANCE: Building a proximal resin composite wall yielded smaller shrinkage vectors than the bulk application. Applying a thin flowable liner decreased the shrinkage vectors, even more when building a proximal wall. A thin flowable liner is recommended when building a proximal resin composite wall.

Shrinkage vectors in flowable bulk-fill and conventional composites: bulk versus incremental application.

OBJECTIVES: Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage vectors in flowable bulk-fill and conventional composites. MATERIALS AND METHODS: Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads. In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk "SDR-bulk" (n = 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: "SDR-incremental" and "EvoFlow-incremental." Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm2), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (n = 10). RESULTS: The greatest shrinkage vectors were found in "SDR-bulk" and "SDR-increment2," and the smallest were found in "SDR-increment1-covered" and "EvoFlow-increment1-covered." Shrinkage away from and toward the cavity floor was greatest in "SDR-bulk" and "EvoFlow-increment2," respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane's T2 test, p < 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in "SDR-bulk." CONCLUSIONS: The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor. CLINICAL RELEVANCE: Incremental application remains the gold standard of composite insertion.

Remineralization, Regeneration, and Repair of Natural Tooth Structure: Influences on the Future of Restorative Dentistry Practice.

Currently, the principal strategy for the treatment of carious defects involves cavity preparations followed by the restoration of natural tooth structure with a synthetic material of inferior biomechanical and esthetic qualities and with questionable long-term clinical reliability of the interfacial bonds. Consequently, prevention and minimally invasive dentistry are considered basic approaches for the preservation of sound tooth structure. Moreover, conventional periodontal therapies do not always ensure predictable outcomes or completely restore the integrity of the periodontal ligament complex that has been lost due to periodontitis. Much effort and comprehensive research have been undertaken to mimic the natural development and biomineralization of teeth to regenerate and repair natural hard dental tissues and restore the integrity of the periodontium. Regeneration of the dentin-pulp tissue has faced several challenges, starting with the basic concerns of clinical applicability. Recent technologies and multidisciplinary approaches in tissue engineering and nanotechnology, as well as the use of modern strategies for stem cell recruitment, synthesis of effective biodegradable scaffolds, molecular signaling, gene therapy, and 3D bioprinting, have resulted in impressive outcomes that may revolutionize the practice of restorative dentistry. This Review covers the current approaches and technologies for remineralization, regeneration, and repair of natural tooth structure.

Effects of boundary condition on shrinkage vectors of a flowable composite in experimental cavity models made of dental substrates.

OBJECTIVES: Bond strength to enamel and dentin depends on the bonding approach or condition. This study investigated the effects of the boundary conditions, in terms of the bonding substrate and the bonding condition, on the shrinkage vectors of a flowable composite. MATERIALS AND METHODS: An experimental cylindrical cavity (diameter = 6 mm, depth = 3 mm) consisting of the enamel floor and the surrounding dentin cavity walls was prepared for the "enamel-floor" group. Cylindrical cavities of the same dimensions were prepared with access from the occlusal enamel into dentin and served as controls. Each cavity model group was divided and bonded with two bonding conditions (n = 9): a self-etch (Adper Easy Bond, 3M ESPE) and a total-etch approach (OptiBond FL, Kerr). The composite (Tetric EvoFlow, Ivoclar Vivadent) was mixed with glass beads, applied to the cavity, scanned twice by micro-CT (uncured and cured states). The scans were evaluated by rigid registration, sphere segmentation, and registration for computing shrinkage vectors. RESULTS: The free surface of all restorations moved downward. The shrinkage vectors in the experimental cavity model pointed downward towards the enamel cavity floor, and the net axial movement was downward. In the control group, shrinkage vectors additionally moved upward, away from the cavity floor. The effect of the bonding substrate and the bonding condition was investigated for the shrinkage vectors and the axial movement (univariate ANOVA). CONCLUSION: The bonding substrate, enamel, influenced the shrinkage vectors' direction, while the bonding condition caused only variations in the magnitude. CLINICAL RELEVANCE: Bonding to enamel influences shrinkage vectors' direction, while the bonding condition plays only a minor role. Graphical abstract ᅟ.

Microtensile bond strength, 4-point bending and nanoleakage of resin-dentin interfaces: Effects of two matrix metalloproteinase inhibitors.

Chronic degradation of hybrid layer collagen by matrix metalloproteinases (MMPs) jeopardizes resin-dentin interfacial integrity and limits the durability of dental restorations. The 4-point bending strength (BS) is a valid but uncommon method of testing the mechanical behavior of resin-dentin interfaces. The present study aims to analyze the influence of two matrix metalloproteinase inhibitors on microtensile bond strength (µTBS), BS and nanoleakage. A total of 48M were divided into three groups according to bonding procedure. Teeth were horizontally sectioned to produce a flat dentin surface. In the control group, etch-and-rinse Prime&Bond One (Dentsply) bonding was used; in the self-etch group, methacryloyloxydodecylpyridinium bromide (MDPB)-containing Clearfil SE Protect (Kuraray) was used; and in the benzalkonium chloride (BAC)-etch group, BAC-etchant (Bisco) was used. A Ceram.X-One (Dentsply) composite was built as three successive layers and was light-cured. Samples were sectioned to produce microrods that were randomly divided into two groups for analysis at baseline and after 6 months of water immersion (n = 32), plus one slab for nanoleakage analysis (n = 8) via scanning electron microscopy (SEM) and digital image analysis (Fiji). Data were analyzed using the Weibull distribution and a mixed-model ANOVA with a post hoc Tukey test. All groups showed deterioration of the initial bonds. The self-etch group had a worse baseline µTBS than the control but had the best BS after aging. BAC-etch did not improve bond stability of etch-and-rinse adhesive. The µTBS and BS test results after aging were moderately correlated. Mixed fractures prevailed with regard to µTBS, whereas adhesive fractures dominated with regard to BS. Nanoleakage was not eliminated in any group and increased after aging. MDPB self-etch resisted bond degradation better than etch-and-rinse adhesives, even after BAC-etching. Integrating BS in studies of µTBS and nanoleakage might provide more clinically relevant outcomes for predicting the performance of dental adhesives.

Shrinkage vectors of a flowable composite in artificial cavity models with different boundary conditions: Ceramic and Teflon.

Polymerization shrinkage of dental resin composites leads to stress build-up at the tooth-restoration interface that predisposes the restoration to debonding. In contrast to the heterogeneity of enamel and dentin, this study investigated the effect of boundary conditions in artificial cavity models such as ceramic and Teflon. Ceramic serves as a homogenous substrate that provides optimal bonding conditions, which we presented in the form of etched and silanized ceramic in addition to an etched, silanized and bonded ceramic cavity. In contrast, the Teflon cavity presented a non-adhesive boundary condition that provided an exaggerated condition of poor bonding as in the case of contamination during the application procedure or a poor bonding substrate such as sclerotic or deep dentin. The greatest 3D shrinkage vectors and movement in the axial direction were observed in the ceramic cavity with the bonding agent followed by the silanized ceramic cavity, and smallest shrinkage vectors and axial movements were observed in the Teflon cavity. The shrinkage vectors in the ceramic cavities exhibited downward movement toward the cavity bottom with great downward shrinkage of the free surface. The shrinkage vectors in the Teflon cavity pointed towards the center of the restoration with lateral movement greater at one side denoting the site of first detachment from the cavity walls. These results proved that the boundary conditions, in terms of bonding substrates, significantly influenced the shrinkage direction.

Effects of occlusal cavity configuration on 3D shrinkage vectors in a flowable composite.

OBJECTIVE: The objective of this study was to investigate the effects of cavity configuration on the shrinkage vectors of a flowable resin-based composite (RBC) placed in occlusal cavities. MATERIALS AND METHODS: Twenty-seven human molars were divided into three groups (n = 9) according to cavity configuration: "adhesive," "diverging," and "cylindrical." The "adhesive" cavity represented beveled enamel margins and occlusally converging walls, the "diverging" cavity had occlusally diverging walls, and the "cylindrical" cavity had parallel walls (diameter = 6 mm); all cavities were 3 mm deep. Each prepared cavity was treated with a self-etch adhesive (Adper Easy Bond, 3 M ESPE) and filled with a flowable RBC (Tetric EvoFlow, Ivoclar Vivadent) to which had been added 2 wt% traceable glass beads. Two micro-CT scans were performed on each sample (uncured and cured). The scans were then subjected to medical image registration for shrinkage vector calculation. Shrinkage vectors were evaluated three-dimensionally (3D) and in the axial direction. RESULTS: The "adhesive" group had the greatest mean 3D shrinkage vector lengths and upward movement (31.1 ± 10.9 µm; - 13.7 ± 12.1 µm), followed by the "diverging" (27.4 ± 12.1 µm; - 5.7 ± 17.2 µm) and "cylindrical" groups (23.3 ± 11.1 µm; - 3.7 ± 13.6 µm); all groups differed significantly (p < 0.001 for each comparison, one-way ANOVA, Tamhane's T2). CONCLUSION: The values and direction of the shrinkage vectors as well as interfacial debonding varied according to the cavity configuration. CLINICAL RELEVANCE: Cavity configuration in terms of wall orientation and beveling of enamel margin influences the shrinkage pattern of composites.